enter questions about physics here, and i or someone else will do our best
to help you

85 responses total.

i get to ask the first question of the conf!  here goes.  if speed is the
dirivitive of distance, and v' is acceleration, what is a', or the rate of
change of acceleration?  this has been bugging me, as i know there is such
a thing.  i use it in my car all the time.  i accelerati, and i accelerate
faster and faster , until i reach a high ehough rpm, and then shift and
start over.  so, what is the dirivitive of acceleration, or the rate of
change of acceleration?

The expression "accelerate faster and faster" may not mean that the
acceleration is increasing, though the speed is. What you are asking about
is the first derivative of acceleration, which is the second derivative of
velocity (and the third derivative of position with respect to time).

If you record your speed as you accelerate, you can estimate the
acceleration. Say, plot the speed vs. time. If the line is straight, your
acceleration is constant. If it is concave downward, the acceleration is
decreasing, even though the speed is increasing. It is possible that the
curve would be "S" shaped, which could mean that as the speed starts to
increase, the engine efficiency increases, so initially the acceleration
increases, but eventually friction will take over, and the acceleration
will decrease. (It might be easier to measure the times at which you are
going 10, 20, 30, etc mph, and plot that.)

The rate of increase in acceleration will also be felt as in increasing
pressure of the seat on your back - or, how far you are pushed back into
the seat. If you feel a constant force, your acceleration is constant. I
have very definitely noticed the "S" shaped pattern of acceleration when
taking off in an airplan, where engine efficient does increase very
dramatically as speed starts to increase. 

i realize all this.  i just finished physics mechanics, and we had many
hours of this kind of thing.  what i was asking, if i was unclear, is what
the first dirivitive of acceleration is *called*, other than the rate of
change of acceleration.  (one defination of dirivitive)

I do not recall ever hearing a separate *name* for the acceleration of the
acceleration. 

I have heard a' referred to as the *jerk*, and have been told that it is
really high jerk which hurts you when you're in a car accident, not high
speed or high decelleration.

Can you cite a source for that? Its not in any reference I have at hand.
It is a very descriptive term for a', though.

My source was a math TA peer of mine.  I'll write to him and see if he
knows a book it's in.

sounds about right.  i was under the impression that it was wiplash, or in
other words, inertia.  still, it could quite conceivably be both.

Inertia is a well, and anciently, defined physical concept. Wiplash
involves differences of acceleration of components of a flexibly coupled
body. However, the term "jerk" has some drawbacks. For example, someone in
a test vehicle might say, "We sure have a lot of jerks here."

I, too, have heard "jerk" used to describe da/dt.
I find it difficult to believe that da/dt is relevant to collision injuries.
The actual injury is done by a (not da/dt and not v), although the amount of
'a' is closely related to the 'v' you were doing before the collision,
since the collision reduces v to 0 in the same short delta-t.

So for collision purposes, v, a, and da/dt are kinda proportional (t
being roughly constant, though not quite, depending on car crumple factors).
The force on the body parts is the injury inducement factor, and
f=ma and m is constant, so I'd say the injury was proportional to a.

Going from a low rate of deceleration to a high one causes differential
displacement of body parts, depending on their mass, elasticity, etc.
It may be that a *sudden* differential displacement may cause damage
that a slower differential displacement would not, perhaps because
of the ability of the body to respond at a finite speed (reaction time).

We probably should try not to get too sidetracked here.  This is the tutoring
conference after all.  But since no one's asking questions ...
Re #10:  I can imagine that if I were to put a wieght on top of someone,
then gradually increase its mass, the mass could get quite big before any
damage would be done.  Thus the force, when increasing slowly, is more
tolerable.  If however you were to increase the force quickly, by adding a
whole lot of weight all at once, that would do some damage, I think.  I'm
just speculating here, I haven't tried it. :)

I asked my ex-peer and he said he heard the term "jerk" from a physics TA
he knew, and he doesn't have a reference for it. :(

ask a simple question...  :)

I look upon this item as a room full of physics tutors. We are just
chatting, waiting for a tutee to come in. We need to advertise 
tutoring, I guess, and tell people that have questions to just
interrupt. Re #13: instructors generally hope the students don't
hear when they mumble "jerk" ;->.

this is true.  *HEY!!  IF YOU HAVE A QUESTION, BUTT IN!!  WE'RE JUST
PLAYING AROUND UNTIL SOMEONE ASKS A QUESTION!!!*  there.  i hope that
helps.  also, i'll go remention it in agora.

This response has been erased.

I suppose that's an alternate definition.  :)

Ok.  I've got a question to get ya'll going.

What are the parts of the unified theory and what's missing at
this point?

definately gravity, and i think time too.  what else?

I know there's seven parts, let me see if I can remember most:

-Mass/energy
-Gravity
-Electromagnetism
-Strong nuclear force
-Weak nuclear force

I remember reading about this in Steven Hawkings' book.  That was a 
while ago and I don't recall all the details.

Ditto on Steven Hawking.

Well, this seems to be a more or less dead cf.  Maybe it'll pick up when
people get out of the review and into the new stuff.  How is it that both
of the items I have entered in my Grex career are duds?

Maybe it needs advertising? You could try an announcement now and then
in agora, to remind users that this service is available.

That would be kinda hard, as I have been converted by carson, and don't do
agora.  Nothing philosophical or anything, I just don't have time.

You don't have to "do" agora, to advertise there. You don't have to
read anything. 

I supose so.  Okay, I'll advertize in agora.

I am wondering if anyone here knows of any books relating to the physics and
chemistry of CO2 exchange across aquatic plantDoes anyone know of a book about
plumbing that is written for nonplumbers but gives some information on fluid
dynamics. 

Cool question!!! I bet it would be fascinating knowledge.

Plumbing is a matter of following the Code, and there are a lot of
self-help books on that (visit any hardware store). Fluid dynamics
is the mathematical description of fluid flow, and there are a lot
of books on that - *not* in hardware stores. There is certainly need
for an understanding of fluid dyamics to do the "plumbing" in new
technology - where a Code has not been developed - but less so in
established technology. So the question is, what level of fluid dynamic
information do you seek for what level of plumbing applications?

I am looking for a watered down version of the fluid dynamics.  I knwo codes
differ from regions so I want a more general book to work my way back into it. 
I am looking at replacing pipes they range from 6" pipe on down I need to also
take into account desired flow rates and pressures.  Much of the work is
straight forward and I could do it without any problem.  I want to have an idea
of how a  plumber would do it though.  I am looking at filtration systems along
with the  plumbing.  I work with swimming pools if thats any help.  I do not
want to get heavily into fluid dynamics if I don't have to.  That is why I want
a watered down version.

Drat! I just threw out a commerical booklist for the construction
industries, which is sent to me now and then. These are not the sort of
books (or booklist) usually kept in general libraries, unfortunately. A
handbook for Mechanical Engineers would have tables for a lot of this, but
not usually "branching networks" formulae. There are computer programs for
analyzing piping networks (but these are usually very expensive, unless
written for school use). I'm thinking, I'm thinking! 8). Maybe you can get
some ideas out of this, and meanwhile I'll look in some other sources. 

Hmmm... Feb 10.  Long time ago.  I wonder if this will ever pick up?  I
don't really have any questions, as I am between physics classes.

Is this the place to ask if anyone knows of documented serious scientific
studies going on with anti-gravity?  Any suggestions of books to read?
I'm a novice on the subject, and not a physics student, but curious.

"Anti-gravity" is science fiction. Or, if you wish, pseudo-science. There
is a discussion of some aspects of the "anti gravity" fad, in _Fads and
Fallacies in the Name of Science_, by Martin Gardner (Dover, 1957). I
would not doubt that there are still current threads of it in the occult
literature. 

Surprisingly enough, Rane, you are not that far off.  I have not heard 
anyone use the term "antigravity".  Don't even really see much need for it,
but I have recently heard people talking about anti-energy of one sort or
another; a sort of metaphysical reversal and nullification.  Odd.

Kami, I am never very "far off" - except when I am far out ;->. 
Hmmm...  (energy) "reversal and nullification" does sound very
metaphysical. Could you give an example of what it is supposed to
mean? 

I wonder if Barry went and read Gardner, and that's why we didn't
hear further from him. Barry?

Rane, this business of reversals- I wonder if the people who were showing
it to me used the term "inversion"?- is new to me.  I don't know a whole
lot about it.  It's not just like water putting out a fire, it's more like
a thing becoming its opposite; like getting an ice-burn, you know? But I
don't want to ramble where I haven't enough information.  Bet I could find
a way to understand and explain it if I had more physics...

This response has been erased.

- Backtalk version 1.3.30 - Copyright 1996-2006, Jan Wolter and Steve Weiss